1. Field of the Invention
This invention relates generally to the fabrication of a giant magnetoresistive (GMR) read head and more particularly to the fabrication of a top spin-valve GMR read head having a novel conducting lead overlay (LOL) design.
2. Description of the Related Art
The spin-valve GMR read head configuration has become commonplace in the prior art. Top spin valves, bottom spin valves and dual spin valves are but some of the variations to be found. In its most essential form, a spin valve consists of two magnetized layers, typically layers of ferromagnetic material, separated by a non-magnetic spacer layer, usually formed of copper. One of the magnetized layers, the “pinned” layer, has its magnetic moment fixed in space, while the other magnetized layer, the “free” layer, has a magnetic moment that is free to move in response to the magnetic fields of external storage media. The angle between the free and pinned magnetizations produces variations in the resistance of the spin valve as a result of there being unequal scattering cross-sections for spin up and spin down conduction electrons. It is these resistance variations that are used to “read” the stored information. The pinned layer has its magnetic moment pinned by a “pinning” layer, which is typically a layer of antiferromagnetic material that is formed in direct contact with the pinned layer. The “bottom” spin valve has its pinned layer at the bottom of the configuration (the pinning layer is nearest the substrate), whereas the “top” spin valve has its pinned layer at the top of the configuration (the pinning layer essentially caps the configuration). Two other material layers are typically formed, one over the other, to either side of the configuration: a current lead layer and a longitudinal magnetic bias layer. The current leads provide a sensing current, which produces voltage variations across the spin valve as a result of the resistance variations. The longitudinal magnetic bias layers stabilize the domain structure of the free layer, making it less sensitive to external noise. FIG. 1 shows a very schematic sketch of a prior art spin valve sensor (either top or bottom type) with conducting leads and longitudinal biasing layers in place. In this particular depiction, the bias layers (2) contact steeply sloping sides of the sensor element (4) to form what is termed a “contiguous junction,” while the conducting leads (6) overlay both the bias layers and the top of the sensor element to form a “lead overlaid” (LOL) design.
A more recent variation on both the top and bottom spin valve configuration is the use of a synthetic antiferromagnetic pinned (SyAP) layer in place of the single ferromagnetic pinned layer. The synthetic layer is, typically, a three layer lamination comprising two ferromagnetic layers separated by a thin non-magnetic coupling layer, typically a ruthenium layer. The two ferromagnetic layers are magnetized in mutually antiparallel directions and held that way by antiferromagnetic exchange coupling across the non-magnetic coupling layer in combination with an antiferromagnetic pinning layer formed on the SyAP. For descriptive purposes, the two ferromagnetic layers will be designated AP1 and AP2, where AP1 is the layer nearest the free layer (typically formed on the copper layer that separates the free and pinned layers.) The SyAP has many advantages over the single ferromagnetic pinned layer, which are not germane to this discussion. The increasing use of the SyAP, however, is of importance, since the present invention will advantageously affect the operation of a SyAP top spin valve element.
For an LOL to function, the lead resistance must be much smaller than that of the GMR stack. In addition, the LOL design must satisfy at least the following three criteria if the sensor is to operate in a maximally advantageous fashion. First, there must be good electrical contact between the LOL and the main portion of the sensor element, i.e. the [free/Cu/AP1] portion of the sensor. This will insure adequate current through the active region of the sensor and strong voltage variations that are easily sensed. Second, the LOL region of the sensor should have a low GMR ratio (the ratio of resistance variation to resistance, dR/R). It is desirable to have the active width of the sensor (the region that reads the narrow tracks of the storage medium) sharply defined in terms of maximum GMR ratio. If the lead region has a low GMR ratio, it enhances the definition of the width. Additionally, if the region of the sensor contacted by the leads also has a high GMR ratio, it will contribute to undesirable side reading of recorded tracks not being accessed. Third, the act of fabricating the lead layer must not damage the free layer. In other words, the process of contiguous junction formation and lead layer deposition must not damage the free layer in the region of the junction and the overlay.
Kakihara (U.S. Pat. No. 6,201,669) provides a spin-valve type read element in which the lead layers are formed both beneath and on the sides of the element. The lead layer formation so provided allows the upper surface of the read head to be flatter.
Saito et al. (U.S. Pat. No. 5,869,963) provides a spin valve sensor formed of multiple spin valve laminates and using PtMn as the antiferromagnetic layer which allows lower annealing temperatures. The longitudinal bias layers and the conductive lead layers are still formed basically in accord with the contiguous junction and lead overlay configuration discussed above and illustrated in FIG. 1 herein.
Yuan et al. (U.S. Pat. No. 5,705,973) provides a dual spin valve formation with improved biasing of the free layer by forming pinned layers both above and below it. The longitudinal biasing and lead formation follow the standard contiguous junction process, wherein the junction shape is produced by ion-milling, with the milling process halted at the antiferromagnetic layer beneath the spin valve formation.
Gill et al. (U.S. Pat. No. 5,828,530) provides a spin valve sensor antisymmetrically located between upper and lower shield layers so that image currents in said shield layers cancel the effects of fields produced by the sense current within the sensor, which latter fields have the undesirable effect of stiffening the magnetic moment of the free layer. The resulting formation has an unusual disposition of its conducting leads, wherein one lead is beneath the spin valve and another is above it. The longitudinal bias layers are still disposed to either side of the spin valve.
None of the prior art structures address the three criteria of advantageous LOL formation: 1) good electrical contact, 2) low GMR ratio in overlay region and 3) non-damaging lead formation. Neither do any of these structures provide an SyAP spin valve, which is a highly advantageous design of wide recent use. It is to precisely the meeting of these three criteria, particularly as they apply to an SyAP design, that the present invention is directed.